1. Field of the Invention
The present invention relates to a camera and a focussing method for the same. More particularly, the present invention relates to a camera which is adapted to plural types of photo films having different thickness and in which an object to be photographed can be focussed precisely and easily, and a focussing method for the same.
2. Description Related to the Prior Art
A roll photo film of a Brownie size is not associated with any cassette or cartridge, but has light-shielding backing paper, which is wound about a roll of photo filmstrip in a form of a commercially sold product. There are two types, 120 and 220. Those are equally wide. The 120-type roll photo film includes the backing paper longer than a photo filmstrip. The backing paper is constituted by three portions that is a leader portion, a backing portion and a trailer portion. The photo filmstrip is exactly overlaid on the backing portion, and located between the leader portion and the trailer portion. The 220-type roll photo film has leader paper and trailer paper, which are respectively secured to a front end and a rear end of the photo filmstrip.
There are plural types of photo film gates used in a camera, including a pressure type and a tunnel type. The pressure type has a pressure plate, which presses the photo film against photo film rails. The pressure type has a feature in that an emulsion surface of the photo filmstrip is not very flat due to a curling tendency of the photo film to curl in a direction rendering its back surface convex. In the tunnel type, a space size or thickness of a photo film passageway or channel defined between the pressure plate and the photo film rails is determined greater than the thickness of the photo film, so that play is created in which the photo film can be slightly shifted. This makes it possible to keep flat an emulsion surface of the photo filmstrip.
In the camera incorporating the tunnel type of photo film gate, a proper in-focus position is expectedly located in a position slightly deviated backwards behind faces of the photo film rails, nearer to the photo film.
In relation to the Brownie photo film, the 120-type photo film is thicker than the 220-type photo film by a difference as much as the thickness of the backing paper. It is necessary in the camera to change over a space size of the photo film passageway between the 120- and 220-type photo films, for the purpose of setting an emulsion surface of the photo filmstrip at a properly in-focus position.
To change over the space size of the photo film passageway, various mechanisms are known. In a camera known as New Mamiya 6 (trade name, manufactured by Mamiya P Co., Ltd.), the pressure plate inside a back lid is rotated by 90 degrees after the back lid is opened. This rotation causes the pressure plate to move back and forwards. When the pressure plate is set in a position for the 220-type photo film, the pressure plate comes in contact with plate contact rails. When the pressure plate is set in a position for the 120-type photo film, the pressure plate comes slightly away from the plate contact rails. In a camera known as Fuji GSW 680 III Professional (trade name, manufactured by Fuji Photo Film Co., Ltd.), the pressure plate is removed from the back lid after the back lid is initially opened. The pressure plate is turned over back to front, and mounted again on the back lid so as to change over the photo film passageway in the same way. In a camera known as Fuji Film GA 645 Professional (trade name, manufactured by Fuji Photo Film Co., Ltd.), the pressure plate is manually pushed toward the back lid and slid in the photo film transport direction while the back lid is opened. The photo film passageway is changed similarly.
In the camera for Brownie photo films according to the prior art, the back lid must be opened to operate the pressure plate directly before the photo film passageway can be changed over. If a user becomes aware that the pressure plate is positioned differently from what he or she intends after loading of the photo film and closing of the back lid, it is impossible to reset the position of the pressure plate properly. If the pressure plate is positioned differently from the way suitable to the photo film being loaded, there occur serious problems. An image cannot be focussed sharply. The photo film is likely to be scratched.
The 220-type photo film has the greater number of available frames than the 120-type photo film. When the pressure plate is positioned for the 220-type photo film, a frame counter of the camera is also changed over to have a wider counting range. If the pressure plate is positioned erroneously in the camera with this structure, there occurs problems in that photographing operation may be stopped before using up all the available frames, or that the entirety of the photo film cannot be wound up in a final step after taking exposures.